This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-153387, filed May 24, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a permanent magnet type reluctance electric motor which is small-sized, and capable of a high output and a varying speed operation in a wide range from a low-speed to a high-speedrotation, achieved by composite permanent magnet.
2. Description of the Related Art
FIG. 1 is a cross sectional diagram directed in a diametrical direction, showing an example of the structure of a conventional reluctance motor.
As shown in FIG. 1, the reluctance-type electric motor includes a stator 1 made of a stator iron core 2 made by laminating electronic steel plates, and having armature coils 3 placed inside slots 7, and a rotor 10 placed on an inner side of the stator 1 and made of a rotor iron core 4 having projections and recesses.
The conventional reluctance electric motor having such a structure as described above does not require a coil for creating a field magnet in the rotor 10, and thus the rotor 10 can be made of only the rotor iron core 4 having projections and recesses.
Therefore, the reluctance electric motor has a simple structure and is of a low cost.
Next, the principle of generating an output from the above-type of reluctance electric motor will now be described.
In the reluctance electric motor, the rotor 10 has projections and recesses. With this structure, the magnetic reluctance is small at a projecting portion, whereas the magnetic reluctance is large at a recess portion.
In other words, the magnetic energy which is stored by allowing an electrical current to the motor coil 3 differs between gap sections on the projecting and recess portions. Due to the difference in the magnetic energy, an output is generated.
It should be noted here that the shapes of the projecting portions and recess portions may be arbitrary as long as they can generate projections and recesses not in terms of geometrically but magnetically (that is, the magnetic reluctance as well as the magnetic flux density distribution differ from one position to another in the rotor 10).
In the meantime, there is another type of a high-performance motor as a permanent magnet electric motor. The permanent magnet electric motor has an armature similar to that of the reluctance electric motor, but the rotor is provided with permanent magnets arranged around substantially the entire circumference of the rotor iron core and the rotor itself.
Incidentally, such a conventional electric motor as described above entails technical drawbacks to be solved.
That is, the reluctance electric motor has projections and recesses on the surface of the rotor iron core 4, and therefore the magnetic reluctance differs depending on the rotating position, and the magnetic flux density changes as well. Then, due to the changes, the magnetic energy changes as well to generate an output.
However, as an electric current increases, the regional magnetic saturation in a projecting portion of the rotor iron core 4, which serves as a magnetic pole, is enlarged (the projecting section being a section where the magnetic flux easily passes through, and to be called d-axis hereinafter).
As a result of this, the magnetic flux which leaks to the recess portion of teeth, which is an in-between of magnetic poles, is increased, (the recess section being a section where the magnetic flux does not easily pass through, and to be called q-axis hereinafter) and therefore a significant magnetic flux is decreased, thereby lowering the output.
Or in terms of the magnetic energy, due to the leaking magnetic flux created by the magnetic saturation of the iron core teeth, the change in the gap magnetic flux density becomes smooth, and the change in the magnetic energy becomes small.
Therefore, the increasing rate of the output with respect to the current is decreased, and the output is eventually saturated. Further, the leaking flux of the g-axis induces a reactive voltage, and therefore the power factor is decreased.
Further, there is another type of a high-performance motor, which is a permanent magnet electric motor in which rare earth permanent magnets of a high magnetic energy product are applied.
The permanent magnet electric motor has permanent magnets on the surface of the rotor iron core. With this structure, the permanent magnets of a high energy are applied to the field magnet, and thus a high magnetic field can be formed in a cavity of the electric motor, thereby making it possible to realize a small-sized but high-output type.
However, since the flux of the permanent magnets is constant, the voltage induced to the motor coil at a high-speed rotation, becomes larger in a proportional manner.
Therefore, in the case of performing a variable speed drive in a wide range from a low speed to a high-speed rotation, the field magnet flux cannot be decreased. Therefore, when the power voltage is set constant, it is difficult to perform a constant output drive at a speed twice as high or more of the base speed.
An object of the present invention is to provide a small-sized and high-output permanent magnet type reluctance electric motor capable of a variable speed operation in a wide range from a low-speed to high-speed rotation.
In order to achieve the above-described object, there is provided, according to the present invention, a permanent magnet type reluctance electric motor comprising: a stator including a stator iron core and having armature coils placed inside slots, and a rotor provided with a plurality of magnetic barriers formed by cavities and placed on an inner side of the stator in such a manner that sections where a magnetic flux can easily pass (d-axis) and sections where a magnetic flux cannot easily pass (q-axis) are alternately formed, and made of a rotor iron core having permanent magnets in cavities, wherein the rotor satisfies a relationship of PL/2xcfx80RWqavexe2x89xa7130, where Wqave [m] indicates an average thickness of the rotor iron core on an outer side in a radial direction of the rotor with respect to cavities arranged in a q-axis direction, L [m] indicates a width in a circumferential direction of the cavities, P indicates the number of poles and R [m] indicates the radius of the rotor.
Therefore, in the permanent magnet type reluctance electric motor of the present invention, the rotor satisfies a relationship of PL/2xcfx80RWqavexe2x89xa7130. With this structure, a high torque can be obtained, and therefore it is possible to perform a variable speed drive at a high output in a wide range from a low speed to a high-speedrotation.
Further, in the permanent magnet type reluctance electric motor recited in claim 1 of the present invention, the rotor is formed to have a structure which satisfies a relationship of: PL/2xcfx80RWqave xe2x89xa7200.
As described above, in the permanent magnet type reluctance electric motor of the present invention, the rotor satisfies a relationship of: PL/2xcfx80RWqavexe2x89xa7200. With this structure, an even higher torque can be obtained, and therefore it is possible to perform a variable speed drive at a higher output in a wide range from a low speed to a high-speedrotation.
Further, in the permanent magnet type reluctance electric motor recited in claim 1 or 2 of the present invention, the cavities arranged in the q-axis direction are made to go through to an outer circumferential portion in a radial direction of the rotor.
Thus, in the permanent magnet type reluctance electric motor of the present invention, the cavities arranged in the q-axis direction are made to go through to an outer circumferential portion in the radial direction of the rotor. With this structure, at a low-speed rotation, an especially high torque can be obtained, and therefore it is possible to perform a variable speed drive at a higher output and in a wide range from a low speed to a high-speed rotation.
Further, there is provided, according to the present invention, a permanent magnet type reluctance electric motor comprising: a stator including a stator iron core and having armature coils placed inside slots, and a rotor provided with a plurality of magnetic barriers formed by cavities and placed on an inner side of the stator in such a manner that sections where a magnetic flux can easily pass (d-axis) and sections where a magnetic flux cannot easily pass (q-axis) are alternately formed, and made of a rotor iron core having permanent magnets in cavities, wherein the rotor satisfies a relationship of WdminP/2xcfx80Rxe2x89xa765, where Wdmin [m] indicates a minimum distance between a cavity arranged in the q-axis direction and a permanent magnet, P indicates the number of poles and R [m] indicates the radius of the rotor.
Therefore, in the permanent magnet type reluctance electric motor of the present invention, the rotor satisfies a relationship of WdminP/2xcfx80Rxe2x89xa765. With this structure, a high torque can be obtained, and therefore it is possible to perform a variable speed drive at a high output in a wide range from a low-speed to a high-speed rotation.
Further, in the permanent magnet type reluctance electric motor recited in claim 4 of the present invention, the rotor is formed to have a structure which satisfies a relationship of: WdminP/2xcfx80Rxe2x89xa787.
As described above, in the permanent magnet type reluctance electric motor of the present invention, the rotor satisfies a relationship of: WdminP/2xcfx80Rxe2x89xa787. With this structure, an even higher torque can be obtained, and therefore it is possible to perform a variable speed drive at a higher output in a wide range from a low-speed to a high-speed rotation.
Further, there is provided, according to the present invention, a permanent magnet type reluctance electric motor comprising: a stator including a stator iron core and having armature coils placed inside slots, and a rotor provided with a plurality of magnetic barriers formed by cavities and placed on an inner side of the stator in such a manner that sections where a magnetic flux can easily pass (d-axis) and sections where a magnetic flux cannot easily pass (q-axis) are alternately formed, and made of a rotor iron core having permanent magnets in cavities, wherein the rotor satisfies a relationship of 95xe2x89xa6WdaveP/2xcfx80Rxe2x89xa6160, where Wdave [m] indicates an average distance between a cavity arranged in the q-axis direction and a permanent magnet, P indicates the number of poles and R [m] indicates the radius of the rotor.
Therefore, in the permanent magnet type reluctance electric motor of the present invention, the rotor satisfies a relationship of 95xe2x89xa6WdaveP/2xcfx80Rxe2x89xa6160. With this structure, a high torque can be obtained, and therefore it is possible to perform a variable speed drive at a high output in a wide range from a low-speed to a high-speed rotation.
Further, in the permanent magnet type reluctance electric motor recited in claim 6 of the present invention, the rotor is formed to have a structure which satisfies a relationship of: 110xe2x89xa6WdaveP/2xcfx80Rxe2x89xa6130.
As described above, in the permanent magnet type reluctance electric motor of the present invention, the rotor satisfies a relationship of: 110xe2x89xa6WdaveP/2xcfx80Rxe2x89xa6130. With this structure, an even higher torque can be obtained, and therefore it is possible to perform a variable speed drive at a higher output in a wide range from a low-speed to a high-speed rotation.
Further, according to the present invention, the width in the radial direction of a cavity situated in the q-axis direction is increased towards the center in the q-axis direction.
As described above, in the permanent magnet type reluctance electric motor of the present invention, the width in the radial direction of a cavity situated in the q-axis direction is increased towards the center in the q-axis direction. With this structure, an even higher torque can be obtained, and therefore it is possible to perform a variable speed drive at a higher output in a wide range from a low-speed to a high-speed rotation.
Further, according to the present invention, the angle of the permanent magnets is changed so that the distance between a cavity situated in the q-axis direction and a permanent magnet becomes maximum at a position on an inner diameter side of the center of the cavity in the q-axis direction.
As described above, in the permanent magnet type reluctance electric motor of the present invention, the angle of the permanent magnets is changed so that the distance between a cavity situated in the q-axis direction and a permanent magnet becomes maximum at a position on an inner diameter side of the center of the cavity in the q-axis direction. With this structure, an even higher torque can be obtained, and therefore it is possible to perform a variable speed drive at a higher output in a wide range from a low-speed to a high-speed rotation.
Further, there is provided, according to the present invention, a permanent magnet type reluctance electric motor comprising: a stator including a stator iron core and having armature coils placed inside slots, and a rotor provided with a plurality of magnetic barriers formed by cavities and placed on an inner side of the stator in such a manner that sections where a magnetic flux can easily pass (d-axis) and sections where a magnetic flux cannot easily pass (q-axis) are alternately formed, and made of a rotor iron core having permanent magnets in cavities, wherein the rotor satisfies a relationship of 0.45xe2x89xa6Wt/xcfx84xe2x89xa60.8, where xcfx84 [m] indicates the pitch of the slot and Wt [m] indicates the width of the teeth.
Therefore, in the permanent magnet type reluctance electric motor of the present invention, the rotor satisfies a relationship of 0.45xe2x89xa6Wt/xcfx84xe2x89xa60.8. With this structure, a high torque can be obtained, and therefore it is possible to perform a variable speed drive at a high output in a wide range from a low-speed to a high-speed rotation.
Further, in the permanent magnet type reluctance electric motor, the rotor is formed to have a structure which satisfies a relationship of: 0.45xe2x89xa6Wt/xcfx84xe2x89xa60.8.
As described above, in the permanent magnet type reluctance electric motor of the present invention, the rotor satisfies a relationship of: 0.45xe2x89xa6Wt/xcfx84xe2x89xa60.8. With this structure, an even higher torque can be obtained, and therefore it is possible to perform a variable speed drive at a higher output in a wide range from a low-speed to a high-speed rotation.